a) Field of the Invention
The invention relates in general to a kick scooter, and more particularly to a kick scooter having a simple structure and convenient usability that provide a user with a maximum driving force and a maximum velocity of movement.
b) Description of the Related Art
A conventional three-wheel kick scooter chiefly includes an upright control arm and a pair of vehicle frames. The upright control arm includes a handle at an upper end thereof and a front wheel at a lower end thereof. The vehicle frames are disposed with left and right rear wheels at ends thereof, respectively. By treading both feet on left and right footboards of the kick scooter and swinging a user body left and right, a vehicle body of the kick scooter is driven to move forward. Three points of contact are formed by the front wheel and the rear left and right wheels, allowing a user securely step on the left and right footboards. By incorporating twisting of the handle or the body, the upright control arm can be swung left and right. As such, by further respectively applying downward forces on the left and right footboards, the front wheel is propelled to roll forward along a zigzag path to perform a forward motion.
Although the conventional kick scooter above achieves sliding movements as well as exercise for a rider on the kick scooter, through theoretical applications based on machinery mechanics and practical design verifications, the kick scooter may yet be further improved to offer more enhanced performance. For example, referring to FIG. 1, left and right rear wheels 11 and 12 are respectively mounted to rear ends of bearing bars 15, and force receiving positions at which a rider treads on left and right footboards 13 and 14 are respectively at upper parts of the left and right rear wheels 11 and 12. When the rider alternatively applies downward forces F1 and F2 on the left and right footboards 13 and 14, as a left fulcrum 111 and a right fulcrum 121 are respectively formed between the left and right rear wheels 11 and 12 and the ground in contact, a counterclockwise rotary torque is produced at the left footboard 13 due to the moment generated (by an arm d1×the force F1). Similarly, a counterclockwise rotary torque is produced at the right footboard 14 due to the moment generated (by an arm d2×the force F2). At this point, first of all, since the force receiving positions of the left and right footboards 13 and 14 are at the upper parts of the left and right rear wheels 11 and 12 in a way that the left and right footboards 13 and 14 are near the left and right fulcrums 111 and 121 of the left and right rear wheels 11 and 12, the moment generated is smaller on account of a shorter moment arm. Thus, the left and right footboards 11 and 12 cannot be provided with a large rotary torque and a lower overall treading efficiency is obtained.
Secondly, the moment exerted on the left footboard 13 causes a counterclockwise rotary torque and the moment exerted on the right footboard 14 also causes a counterclockwise rotary torque. Owing to the counterclockwise rotary torques exerted on the left and right rear wheels 11 and 12 and frictions generated by the counterclockwise rotary torques against the ground, the downward treading forces may be diminished. Because of the above reasons, the downward treading forces of the rider are diminished, which reduces the efficiency of the downward treading forces and hinders the rider from obtaining a greater velocity of movement.